1. Field of the Invention
This invention relates to injection molding machines and more particularly relates to a sealing member inserted in an injection molding machine for substantial reduction or elimination of leakage of a molten material.
2. Summary of the Prior Art
Hot runner assemblies are previously known and are used for molds having a plurality of mold cavities for injection molding of articles of relatively large surface dimensions. The advantage of hot runner molds is that the material is maintained in the molten state in the channels during the interval between each injection operation and the following one.
Prior art hot runner molds may be divided into two groups, i.e. hot runner manifolds that are one piece and have all the melt channels formed therein and multi-piece manifolds that are connected together with xe2x80x9cbridgexe2x80x9d manifolds. In the multi-piece arrangement, a xe2x80x9cbridgexe2x80x9d manifold connects at least two sub-manifolds. Melt channels in the bridge manifold align with melt channels in the sub-manifolds. Typically, the bridge manifold is connected to a supply of pressurized molten material.
The melt channels in the xe2x80x9cbridgexe2x80x9d manifold must align with the melt channels in the sub-manifolds when they are at a predetermined elevated temperature. The sub-manifolds typically communicate with at least one injection nozzle for the transfer of the molten material to a mold cavity. Due to thermal expansion during heat up of the various hot runner manifolds, relative motion between the xe2x80x9cbridgexe2x80x9d manifold and the sub-manifolds will occur. In accordance with the prior art, the flat surface of the sub-manifold will rub across the flat surface of the xe2x80x9cbridgexe2x80x9d manifold during heat up, and when the desired temperature is reached, the interface between the respective melt channels will align and seal off by virtue of compressive forces that build up during the heat up process. The reliability and repeatability of this seal off has proven to be problematic and leakage of the molten material between the xe2x80x9cbridgexe2x80x9d manifold and the sub-manifold is a recurrent problem.
Therefore there is a need for an improved hot runner system that increases the reliability and repeatability of the seal between separate manifold melt channels.
The primary objective of the present invention is to provide a means for reliably sealing the melt channel interface between a bridge manifold and a sub-manifold.
Another object of the present invention is to reduce the compressive forces generated in a hot runner subsystem during heat up thereby allowing the use of fewer fasteners.
Yet another object of the present invention is to reduce or eliminate the occurrence of galling and/or fretting between plates as they move during heat up.
The foregoing objects are achieved by providing a sealing member or compression disk at the interface of the melt channels between the two manifolds. The sealing member preferably has at least one non-flat surface for concentrating the sealing pressure adjacent the melt channels thereby reducing the forces required to create a reliable seal therebetween.
Further objects and advantages of the present invention will appear hereinbelow.